Microwave scanning antennas



July'14, 1959 Y J. BUTLER MICROWAVE SCANNING ANTENNAS 2 Sheets-Sheet 1 Filed Sept. 17. 1954 lNl/ENTDR JESSE L. BUTLER z- A TTORNEV July 14, 1959 J. BUTLER 2,395,131

MICROWAVE SCANNING ANTENNAS Filed Sept. 17. 1954 2 Sheets-Sheet 2 l I i t I pom/2124110 1. ASSUMED VERTICAL l SAME AS 0 l RC RC [25 R 2. I Q I RC I EC I ,1 \Rcl I, MC g; MC MC 2 MC @5 R 2. R 3 ,2; C RC I 1' RC2; [xi I, E RC/:0 RC3 3 RC l I l l l 5; UP E EIGHT E DOWN E LEFT E UP RC, EFFECTIVE RADIATION CENTER or: 01.5 *I EFFECTYVE RADIATION CENTER OF POLE *2 RC; RC; EFFECTIVE RADIATION CENTER OF POLE 3 MC MECHANICAL CENTER E EC EFFECTIVE CENTER OF RADIATION /NVENTOR JESSE L. BUTLER ATTORNEY MICROWAVE SCANNING ANTENNAS Jesse L. Butler, Nashua, N.H., assignor to Raytheon Company, a corporation of Delaware Application September 17, 1954, Serial No. 457,072

12 Claims. (Cl. 343-754) This application is a continuation-in-part of an application for United States Letters Patent, Serial No. 424,313, filed April 20, 1954, for Antenna, now abandoned.

This invention relates to a microwave scanning antenna and particularly to a rotating tri-element radiator for the purpose of increasing the scan rate threefold for every mechanical revolution of said radiator.

The above increased scan rate is accomplished by using a rotating tri-element radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation. The tri-element radiator is rotated in a microwave energy field, thereby generating an effective conical scan at three times the physical rotational velocity of the tri-element radiator.

Further objects and advantages of this invention will be apparent as the description progresses, reference being made to the accompanying drawings, wherein:

Fig. 1 is a cross-sectional view of an embodiment of the invention that is illustrated in the form of a directional microwave antenna;

Fig. 2, which is section 22 of Fig. 1, illustrates a front view of the tri-element radiator in the form. of a tri-pole radiator;

Fig. 3, which is section 3-3 of Fig. 2, illustrates a cross-sectional view of the tri-pole radiator; and

Fig. 4 is a series of diagrams illustrating how the trielement radiator produces an offset center of radiation that describes a perfect circle about the mechanical center of rotation at a rate which is three times the rate of mechanical rotation.

Referring now to Figs. 1, 2, and 3, there is shown for the purpose of illustration only an embodiment of the tri-element radiator in the form of a tri-pole radiator being used in a suitable antenna system. The tri-element radiator is adaptable to be used in both transmitting and receiving antenna systems.

The tri-pole radiator 10 is placed at the focal point of a reflecting paraboloid 11, said tri-pole radiator 10 being capable of rotating about an axis running through said focal point and the center of said reflecting paraboloid. A circular wave guide 12, having its central line on said axis, is connected to and through the reflecting paraboloid 11 so as to face the tri-pole radiator 10 and thereby illuminate it with microwave energy, said energy being reflected off the reflecting paraboloid 11 and thence into space.

The tri-element radiator can be constructed in a variety of shapes and forms, the only limitation being that three symmetrical radiating elements should be used and so constructed as to make the radiators symmetrical about an axis passing through its center point, saidradiating elements to extend radially from the center point of said tri-element radiator substantially in a plane, thereby being symmetrical about said axis of rotation.

The tri-pole radiator 10, as illustrated, is constructed of five basic parts. A reflector disc 13 is constructed 2,895,131 Patented July 14, 1959 of good conducting material flat on one side having a collar 14 with a set screw 15 on the other side. Located on the flat side of the reflector disc 13 is a spacer 16 constructed of a dielectric material of such a thickness as to separate the reflector disc 13 from three radiating poles 17 which are located on the other side of spacer 16. Said radiating pole 17 is constructed of a good conducting material. Cone disc 18 is constructed of a dielectric material and contains a pin 19 that is used to keep the tri-pole radiator 10 assembled as a unit. Said pin 19 is inserted centrally through and cemented to cone disc 18, poles 17 and reflector disc 13 thereby bonding all the elements of the tri-pole radiator 10 together. Other tri-element configurations will be apparent to those skilled in the art.

The hole in collar 14 is used for the purpose of mounting said tri-pole radiator 10 on shaft 20 of a motorgenerator 21 driving means. Said set screw 15 located in collar 14 is used to lock shaft 20 and tri-pole radiator 10 together. This action maintains the position of the tri-pole radiator 10 with respect to the motor-generator 21 which supplies the rotating means for rotating the tri-pole radiator 10 in the microwave energy field.

Motor-generator 21 is a special device containing a one thousand cycle synchronous motor 22 and a 250-cycle generator 23 on one shaft 20. The motor 22 is used primarily for rotating the tri-pole radiator 10 and the generator 23 is used to give an AC. reference voltage for determining the position of said tri-pole radiator 10 at any specific time. This A.C. generated reference voltage is necessary when it is considered that the three fold scan rate is accomplished by actually having three rotating antennas. It is necessary, therefore, to know at any particular time which antenna is receiving or transmitting energy. The problem is analogous to a lobing antenna where there are three lobes to be identified.

The motor-generator 21 is held firmly by a clamp 24 which is supported by four support brackets 25. These support brackets 25 are connected to reflecting paraboloid 11 thereby maintaining the position of tri-pole radiator 10 at the focal point of reflecting paraboloid 11 by maintaining the position of motor-generator 21 with respect to said reflecting paraboloid 11.

The motor leads 26 for motor 22 are threaded through one of the support brackets 25. The generator leads 27 for generator 23 are threaded through the opposite support bracket 25 for the purpose of reducing interaction between the two sets of leads. Two pivotal holes 31 are located on the rear of reflecting paraboloid 11 so as not to interfere with the reflecting surface of said reflecting paraboloid 11 or wave guide 12. These holes 31 are arranged to be used with outside means for moving reflecting paraboloid 11.

Referring now to Fig. 4, there is illustrated a series of diagrams showing how the tri-element radiator produces an otfset center of radiation about its mechanical center at a rate which is three times the rate of mechanical rotation. For explanation purposes a tri-pole antenna is illustrated, it being understood that the following reasoning applied for any rotating tri-element radiator.

Fig. 4 illustrates a tri-pole antenna in five positions representing 0, 30, 60, and of mechanical rotation. Polarization is assumed to be in a vertical plane and pole 1 is assumed to be vertical in the 0 position for the purpose of this explanation. For each of the five mechanical positions there is shown a corresponding vector diagram illustrating the relative magnitude of radiation for all three poles. To simplify the explanation the following symbols will be used:

RC to be the effective radiation center of pole No. 1;

RC to be the effective radiation center of pole No. 2;

RC to be the effective radiation center of pole No. 3;

MC to be the mechanical center of the tri-element radiator; and

E to be the efiective center of radiation of the tri-pole radiator.

In the position, RC is displaced further from MC in the up direction than RC and RC are displaced in the down direction. Hence, E is up. The vector RG represents a vector equal to the sum of vectors RC and RC In the 30 position, pole 2 receives zero energy since it is at right angles to the plane of polarization, and RC and RC, are displaced to the right of MC. Hence, E is right.

In the 60 position, RC is displaced further in the down direction from MC than RC and RC are displaced in the up direction. Hence, E is down. The vector RC represents a vector equal to the sum of vectors RC and RC In the 90 position, pole No. 1 receives zero energy since it is at right angles to the plane of polarization and RC and RC are displaced to the left of MC. Hence, E is left.

In the 120 position RC is displaced further from MC in the up direction than RC and RC are displaced in the down direction. Hence, E is up. The vector RC represents a vector that is equal to the sum of vectors RC and RC From the cases given above, it can be seen that the beam as represented by E has gone through a complete 360 radiation cycle for every 120 of mechanical rotation of the tri-pole antenna. Since the tri-pole antenna has 120 symmetry, the 360 radiation cycle will occur for every 120 of mechanical rotation, or in other words, there will be produced three complete radiation cycles for every one mechanical revolution. It can be shown mathematically that the amount the beam is offset, which is the distance from E to M is constant for all angular positions of the antenna, and that the beam ofi'set describes a perfect circle about the mechanical center of rotation. The most obvious benefit apparent in this antenna system is that the rotating tri-element radiator can be symmetrically balanced about its axis of rotation, thereby producing no mechanical vibrations.

The embodiment of the antenna system as illustrated in Figs. 1, 2 and 3 is particularly adaptable for use against fast maneuvering targets such as aircraft. The small physical size of the antenna lends itself for convenient installation in aircraft or missiles.

When used as a transmitting antenna the microwave energy is emitted from circular wave guide 12 directly illuminating the rotating tri-pole radiator 10. This microwave energy is then radiated by each of the retating radiating poles 17 so that, for every one mechanical revolution of the tri-pole radiator there is produced three separate radiation patterns sometimes called scans or lobes. This energy is then reflected and radiated into space from the parabolic reflector 11.

This completes the description of the embodiment of the invention illustrated herein. However, many modifications and advantages thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. Accordingly, it is desired that this invention not be limited to the particular details of the embodiment disclosed herein, except as defined by the appended claims.

What is claimed is:

l. A microwave antenna comprising a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, means for rotating said radiator about said axis thereby producing three different directional patterns for each mechanical revolution, and means for directing inicrowave energy to said radiator.

2. A microwave antenna comprising a radiator having three radiating poles symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, means for rotating said radiator about said axis thereby producing three different directional patterns for each mechanical revolution, and means for directing microwav energy to said radiator.

3. A microwave antenna comprising a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, means for rotating said radiator about said axis thereby producing three different directional patterns for each mechanical revolution, and a wave guide disposed substantially on the line of said axis directed substantially at said radiator.

4. A microwave antenna comprising a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, means for rotating said radiator about said axis thereby producing three different directional patterns for each mechanical revolution, a wave guide disposed substantially on the line of said axis directed substantially at said radiator, and means for directing microwave energy to said radiator.

5. A microwave antenna comprising a reflector, a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflector, the line of said axis corresponding to the direction of maximum response of said reflector, means for rotating said radiator about said axis thereby producing three different directional patterns for each mechanical revolution, and means for directing microwave energy to said radiator.

6. A microwave antenna comprising a reflector, a re.- diator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflector, the line of said axis corresponding to the direction of maximum response of said reflector, means for rotating said radiator about said axis thereby producing three different directional patterns for each mechanical revolution, and means for directing microwave energy to said radiator.

7. A microwave antenna comprising a reflector, a radiator having three radiating poles symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflector, the line of said axis corresponding to the direction of maximum response of said reflector, means for rotating said radiator about said axis thereby producing three difierent directional patterns for each mechanical revolution, and means for directing microwave energy to said radiator.

8. A microwave antenna comprising a reflector, a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflector, the line of said axis corresponding to the direction of maximum response of said reflector, means for rotating said radiator about said axis thereby producing three difierent directional patterns for each mechanical revolution, and a wave guide disposed substantially on the line of said axis passing through said reflector, directed substantially at the radiator.

9. A microwave antenna comprising a reflector, a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflector, the line of said axis corresponding to the direction of maximum response of said reflector, means for rotating said radiator about said axis thereby producing three diflerent directional patterns for each mechanical revolution, a wave guide disposed substantially on the line of said axis passing through said reflector, directed substantially at the radiator, and means for directing microwave energy to said radiator.

10. A microwave antenna comprising a reflecting paraboloid, a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflecting paraboloid, the line of said axis corresponding to the direction of maximum response of said reflecting paraboloid, means for rotating said radiator about said axis thereby producing three different directional patterns for each mechanical revolution, and means for directing microwave energy to said radiator.

11. A microwave antenna comprising a reflecting paraboloid, a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflecting paraboloid, the line of said axis corresponding to the direction of maximum response of said reflecting paraboloid, means for rotating said radiator about said axis thereby producing three diflerent directional patterns for each mechanical revolution, a Wave guide disposed substantially on the line of said axis, passing through said reflecting paraboloid directed substantially at the radiator, and means for directing microwave energy to said radiator.

12. A microwave antenna comprising a reflecting paraboloid, a radiator having three radiating elements symmetrically disposed radially, substantially in a plane perpendicular to an axis of rotation, said radiator disposed substantially at the focal point of said reflecting paraboloid, the line of said axis corresponding to the direction of maximum response of said reflecting paraboloid, a motor-generator means for both rotating said radiator about said axis and supplying areference alternating current signal that is directly proportional to the rotation of said radiator, supporting means for holding said motor-genenator means to said reflecting paraboloid thereby maintaining the position of said motor-generator means and said radiator with respect to said reflecting paraboloid, a circular Wave guide having its center line disposed substantially on the line of said axis thereby producing three diflerent directional patterns for each mechanical revolution, passing through said reflecting paraboloid and directed substantially at said radiator, and means for directing microwave energy to said radiator.

References Cited in the file of this patent UNITED STATES PATENTS 

